Op, I've got a Bostic fused G36 which in my opinion the only way to go on that rifle. Cost is higher but the stock block conversion is just off - length of pull too long, rifle looks and shoots weird to me so I'm glad I did that one. I will say I'd never use that gun in a serious SHTF scenario - never bad a problem but cutting and gluing the polymer housing just creates another potential point of failure in my mind (perhaps not in reality but the builders have voiced some cautions as well).
I did choose to go stock block conversion on the UMP and it's great. I'm not a purest HK collector and some won't do anything but a fuse job but the difference on the USC is pretty minimal and to me, the cost benefit of the fuse job isnt there, it looks right and shoulders great. And, I don't ever worry about the fuse job. Best, Matt